The present invention relates to a ball joint.
Ball joints have hitherto been utilized for various machines. One known ball joint is shown in FIG. 6. The ball joint consists of, e.g., a socket a, a bearing b provided therein, a ball stud c accommodated in the bearing b and a metal plug d for preventing removal of the ball stud c. The plug d is placed on a stepped portion c shaped upwardly and inwardly of the socket a. An upper end of the socket a is thereafter caulked inwardly by means of a spinning roller or the like, thereby forming a caulked portion f. The plug d is thus enclosed between the caulked portion f and the bearing b.
FIG. 7 shows an arrangement in which the plug d is not provided. For example, the bearing b is incorporated into the socket a. The ball stud c is set in the bearing b. subsequent to this step, an upper part of the socket a is press-caulked spherically inwards, thus enclosing the bearing (Japanese Patent Laid-Open No. 25657/1976).
The known structure described above, however presents many defects as follows. To be specific, the plug d is indispensable for the ball joint shown in FIG. 6, as a result of which the number of parts increases and the number of assembling steps correspondingly increases. A step of machining the plug d with a given accuracy. It is also therefore required. As a result, manfacturing costs thereof are high. In relation to the ball joint of FIG. 7, there is a problem such that a scatter effect is caused between the socket and the bearing. This means the bearing presses against the spherical surface of the ball stud with excessive intensity, or the caulking strength is insufficient. In a great majority of cases, a press-contact state between the ball stud spherical surface and the bearing is unstable. In consequence, uniform performance of the ball joint cannot be obtained. When caulking the socket, the amount of a caulked portion of the socket is variable. This makes an unstable deformation of the bearing. Consequently, the ability of bearing to hold a ball stud is not constant, with the result that a large number of ball joints will be subject to deterioration.